A surge in human infections of a deadly bird flu in China is prompting increasing concern among health officials around the world. While the human risk of these outbreaks is low at the moment, experts are calling for constant monitoring because of the large increase in cases this season, and because there are worrisome changes in the virus. U.S. officials say of all emerging influenza viruses, this particular virus poses the greatest risk of a pandemic threat if it evolves to spread readily from human to human, according to a report released Friday.

Centers for Disease Control and Prevention officials are developing a vaccine that would target a newly evolving version of the virus.

China is experiencing its largest outbreak of the H7N9 bird flu strain, with at least 460 infections reported since October. About a third of people diagnosed with H7N9 have died of their infections, according to the World Health Organization. Human infections with this type of bird flu were first reported in China in March 2013, and since then, there have been yearly epidemics of human infections.

But this winter, the number of cases is greater than any of the previous four seasons. This year's infections account for more than a third of the 1,258 H7N9 cases that have been reported since 2013. Most human infections involve exposure to live poultry or contaminated environments, especially markets where live birds have been sold. During the previous four waves of H7N9, 88 percent of patients developed pneumonia, 68 percent were admitted to an intensive care unit and 41 percent died, according to a report from the CDC.

“This is the virus we were concerned about in 2013, and now we're seeing these increasing number of cases,” said Daniel Jernigan, who heads the CDC's influenza division, in an interview this week. “This year it came back much stronger, so the numbers of cases we're seeing has already surpassed all the other waves, and the season isn't even over yet.”

In addition, the virus has become more deadly to poultry, which might lead to more severe infections in humans, he said. For all those reasons, officials are watching developments closely.

Among a dozen animal and bird viruses that are not yet circulating widely in people, the H7N9 virus has the greatest potential to cause a pandemic, according to the CDC. That assessment is based on the virus's ability to spread easily and efficiently to people from animals and its ability to cause serious disease.

On Wednesday, WHO officials in Geneva said the risk of sustained human-to-human transmission of H7N9 remains low. The characteristics of the infections and case fatality rate remain similar to previous waves, officials said.

But “constant change is the nature of all influenza viruses,” Wenqing Zhang, who heads WHO's global influenza program, told reporters during a media briefing Wednesday. “This makes influenza a persistent and significant threat to public health.”

One change already underway is that the virus has split into two distinct genetic lineages, with a new branch of the virus family now emerging in the current epidemic, officials said.

That has rendered the H7N9 vaccine stockpiled by the United States less effective against the newly emerging branch, officials said. The CDC is developing an influenza seed virus that can be used by vaccine manufacturers to produce another H7N9 vaccine to match a newly emerging H7N9 strain.

It will take several months to produce and test a new vaccine, a process that will get underway in June and July after vaccine manufacturers complete their work on making seasonal flu vaccine.

Vaccines to protect first responders against the highest-risk bird flu viruses are part of the pandemic flu stockpile maintained by the Biomedical Advanced Research and Development Authority, the agency within the Department of Health and Human Services responsible for providing medical countermeasures to human-made and natural threats, including pandemic influenza and emerging infectious diseases.

Rick Bright, director of BARDA, said manufacturers will be producing enough vaccine to provide 40 million doses, enough to vaccinate 20 million people, he said.

Yep - while we can never tell which one will make the jump, this virus is definitely padding out it's resume nicely. And now it's been consistently found in up to 30% of Chinese wet markets tested - the place where humans seem to be at most risk to become infected. I find it even more disturbing that it's clearly entrenched in Guangdong because of that particular province's past role in the emergence of H5N1 and SARS - all the right conditions appear to be in place there to allow novel strains to further mutate to H2H forms.

"Buy it cheap. Stack it deep""Any community that fails to prepare, with the expectation that the federal government will come to the rescue, will be tragically wrong." Michael Leavitt, HHS Secretary.

Health officials in protective suits put a goose into a sack as part of preventive measures against the H7N9 bird flu at a poultry market in Zhuji, Zhejiang province on Jan. 5, 2014. Reuters file

The CDC has been working on a vaccine against H7N9 just in case it's ever needed and is starting work on a second one now because it's started to mutate.

"It's a cause for concern, that's for sure," Uyeki told NBC News. "The surge in numbers of human H7N9 cases in China is definitely a concern."

The CDC issued a travel notice in January, cautioning travelers to China to stay away from live bird markets. Uyeki said travelers do not need to avoid China but they should be aware that poultry can spread the virus.

Since 2013, H7N9 bird flu has infected 1,258 people, the CDC said. So 460 cases in just five months account for a third of all the cases over four years.

Earlier this week the World Health Organization held a meeting on H7N9 and then issued public reassurances, saying the virus did not appear to have changed in a way that would make it more likely to spread to people or to make it more dangerous to people.

“The surge in numbers of human H7N9 cases in China is definitely a concern.”

Instead, the changes make the virus more dangerous to birds — which could be a good thing.

"These changes make the virus highly pathogenic in birds, meaning that it can cause some severe disease in birds," Dr. Wenqing Zhang, head of WHO's global influenza program, told reporters.

"Previously, H7N9 had only been observed to be 'low pathogenic' in birds, meaning the virus did not cause visible outbreaks of disease in birds," Zhang said.

If an avian influenza virus kills birds, it's bad for poultry farmers but it can give a warning that the virus is spreading. The problem with H7N9 has been that it does not make poultry sick, so it can spread among flocks without people knowing it.

Uyeki is worried that H7N9 has become more widespread in China, spreading silently and infecting more people because it's infecting more birds.

"You could have more cases of human infection even if the risk of poultry-to-human transmission has not changed," he said.

China has been publishing genetic sequences of the H7N9 virus in public databases, but it has not been sharing actual samples of the virus, so it's not possible for U.S. labs to test the virus themselves to see whether it's changed and if so, whether it's more dangerous.

But it's already dangerous. H7N9 is considered a moderate to high pandemic threat, although the CDC and WHO do not think an H7N9 pandemic is about to happen, or even that it is certain to happen.

H7N9 is one of several strains of bird flu that officials are watching because they have the potential to cause a human pandemic.

So far, H7N9 doesn't seem to infect people easily and people who are infected do not seem to spread it to others much. But influenza viruses change quickly and unpredictably, and if one starts passing easily from one person to another it could spread.

“H7N9 viruses have the highest risk score and are characterized as posing moder­ate-high potential pandemic risk.”

"From what we understand, there have been no real changes in the epidemiology or mortality of hospitalized H7N9 cases," Uyeki said.

H7N9 can be deadly when people do get it. It kills more than 40 percent of people who get sick enough to go to the hospital.

It often progresses to pneumonia. And hospitals or clinics treating people infected with H7N9 need to take precautions to make sure patients do not infect anyone else.

"Clinicians should consider the possibility of avian influenza A (H7N9) virus infection in people presenting with respiratory illness within 10 days of travel to China, particularly if the patient reports exposure to birds or poultry markets," the CDC says.

The CDC and WHO are watching the spread of several bird flu viruses that are known to infect people, including H5N1 and H7N2.

"Although the current risk to the public's health from A(H7N9) viruses is low, among the 12 novel influenza A viruses evaluated ... A(H7N9) viruses have the highest risk score and are characterized as posing moder­ate-high potential pandemic risk," the CDC team said in the report released Friday.

I'll also add, an h7n9 pandemic could potentially be worse than an h5n1 pandemic. h5n1 is at least susceptible to Tamiflu and anti-virals, and h7n9 has mutated out of that protection and has now evaded it. We would probably have no defense, other than to wait it out. Could be looking a little grim at the moment.

^thanks, I'm keeping a close (epidemiologist's) eye on this! H7N9 had been low-path (pathogenic in birds), so it didn't cause overt symptoms in poultry & thereby was able to spread far and wide in the Asian poultry husbandry industry. By comparison, H5N1 is high-path, so it makes the birds sick....that is how we find outbreaks & snuff out the flocks when we find them.

Widespread dissemination of H7N9 has always bothered me, because this gives the virus more avian hosts to multiply in, as well as being able to jump into other species (porcine especially) where it can reassert with swine flu viruses. Mixing avian and porcine viruses generates some really nuclear stuff....

The Chinese ag industry makes their own problems by feeding poultry mortalities & even feces to swine without rendering. We basically have a huge "reassortment engine" over there, so it is not a question of if, but when, H7N9 jumps out at us.

Given all of this, the major flu pandemic strains have been H1N1, like the last go-around we had and the 1918 Spanish Flu. H7N9 hasn't shown itself to be very adept at infecting humans and spreading, but this one scares the bejeebers out of me compared to H5N1! (I was always an H5N1 skeptic and remain so today).

Keep your powder dry. We have an idiot for a US President, so if this kindles & takes off someplace like China or Viet Nam, Mr. Trump will try to slam barriers in place. That won't work, and he's trying to de-fund our public health system, which will make it worse. Nuclear warheads don't work well on viruses.

I've been thinking about the swine part of the equation too, Chuck - there are half a billion pigs in China, and their role in the re-assortment of avian and mammalian viruses is well documented. Possessing receptors that both can bind to, they now represent an even more efficient mixing vessel given their vast numbers, the incredibly irresponsible diet we feed them, intimate contact with human handlers who can both infect them and become infected by them, the stress induced immunodeficiency common in intensively raised food animals, and the lack of biosecurity in many breeding facilities. We're giving viruses like H7N9 so many opportunities to kill us in huge numbers, and the sad thing is that we're doing it knowingly.

"Buy it cheap. Stack it deep""Any community that fails to prepare, with the expectation that the federal government will come to the rescue, will be tragically wrong." Michael Leavitt, HHS Secretary.

What I understand-whit the little knowledge I have of this-is that the main reason H7N9 has gotten this big in China (and remains so far a China problem) is that the virus did spread widely (since 2013) via domestic birds that did not get ill themselves.

As far as I did read the human-to-human spread seems to be very limited for now. Also I did not see reports of massive starvation in pigs (other mammals).

If H7N9 would grow into a pandemic there are several steps to take;

-wider spread than China

-more human-to-human cases

The H7N9-virus proberbly still get spread by wild birds-wich can give problems with migrating birds. The epedemic seems to slow down during the summer. It may be a few steps away from becoming a potential pandemic virus, for the moment I think H7N9 may remain a major Chinese problem for the coming years.

Que sera, sera, Whatever will be, will be, The future is not ours to see, Que sera, sera !

I agree, Josh - while we're concentrating on the threat from domestic poultry, I believe there has to be a natural reservoir for H7N9 in China. That could complicate things further, because re-assortment both in the wild and on poultry or pig farms due to poor biosecurity could also lead to the emergence of novel strains.

"Buy it cheap. Stack it deep""Any community that fails to prepare, with the expectation that the federal government will come to the rescue, will be tragically wrong." Michael Leavitt, HHS Secretary.

h7n9 has fairly decent bird to human transmission, and of course kills people in China, which is why we definitely don't want that one spreading as it is. h5n1 would rarely infect humans via bird transmission, and in fact none of them do, except for h7n9.

If any could mix with h1n1, it would probably be h7n9, but either way, it's mutating and evolving nicely on it's own at the moment.

Chinese bird flu fears rise

After a relatively quiet few years, avian flu numbers are rising once again, along with concerns about drug resistance. Andrew Masterson reports.

Poultry farms and markets are strongly linked to the spread of avian flu.

KAREN KASMAUSKI

Genetic changes and a leap in case numbers are fueling concerns that China might be on the brink of a major outbreak of avian flu.

The current Chinese flu season, which kicked off in October last year, has so far seen at least 450 confirmed cases of influenza A(H7N9), a virulent and often lethal form that first emerged in 2013, and is strongly linked to poultry markets.

According to virologist Ian Mackay of the Australian Infectious Diseases Research Centre at the University of Queensland, the period “has seen more human cases than any of the previous three seasons”.

Using data from the Hong Kong Centre for Health Protection, MacKay established that most of the confirmed cases were from five provinces, with Jiangsu the worst hit. Almost all are associated with bird markets, although rare cases of human-to-human transmission have been recorded.

In the first outbreak of A(H7N9) the initial spread was explosive, growing from just three to 111 in two months. Of those, more than 70% became seriously ill and around 27% died.

While acknowledging problems with the quality and reliability of the data, MacKay estimates more recent surges of the same flu have delivered a mortality rate of around 40 per cent. Compared to the last season, he notes, the current tally of confirmed cases “dwarfs by quite a lot”.

Because they have the capacity to spread rapidly, flu viruses are always likely to undergo mutation. While most such changes are likely to be either neutral or harmful to the virus itself, exacerbating worries at present is the fact that A(H7N9) seems to have altered in two significant ways.

“Just lately two viral changes have added to concerns,” says MacKay. “One has seen a viral variant that now causes serious illness in birds. Previously, H7N9 spread through flocks unseen because it didn't cause avian disease.

“Another change has seen up to 9% of tested variants with mutations suggesting they may resist a common class of anti-flu drugs.”

Thankfully, he adds, neither of these changes is known to alter how the virus transmits to humans.

Because of them, though, health authorities are recommending existing vaccines be tweaked to take the new variants into account.

As in past outbreaks the Chinese authorities have moved to close down poultry markets in affected areas. However, says MacKay, there are concerns this time that the spread of infection may have outpaced public health.

“Closing live bird markets has, in the past, been followed by a precipitous decline in human cases,” says. “This season of H7N9 cases spread perhaps too quickly for the response to keep up. Closure of markets confirmed to harbour H7N9-infected poultry may not have occurred in sufficient numbers or fast enough to prevent so many human exposures.”

New figures on flu cases are released each week. Given that the World Health Organisation has described H7N9 as “an unusually dangerous virus for humans”, MacKay is by no means the only scientist keeping a careful eye on the tally.

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